Royal Institution. 321 



the exponent of the entire force of the generating cells, and these 

 could independently produce magnetic force, this latter force would 

 be got from nothing, and perpetual motion be obtained. 



In another case, cited by M. Matteucci, viz. that a piece of zinc 

 dissolved in dilute sulphuric acid gives somewhat less heat than 

 when the zinc has a wire of platinum attached to it, and is dissolved 

 by the same quantity of acid, the argument is deduced, that as there 

 is more electricity in the second than in the first case, there should 

 be less heat ; but, as according to our received theories the heat 

 is a product of the electric current, and in consequence of the 

 impurity of zinc, electricity is generated in the first case molecularly 

 in what is called local action, though not thrown into a general 

 direction, there should be more of both heat and electricity in the 

 second than in the first case ; as the heat and electricity due to the 

 voltaic combination of zinc and platinum are added to that excited 

 on the surface of the zinc, and the zinc should be, as in fact it is, 

 more rapidly dissolved. Other instances are given by M. Matteucci, 

 and many additional cases of a similar description might be sug- 

 gested. But although it is difficult, perhaps impossible, to restrict 

 the action of any one force to the production of one other force, 

 and one only; yet if the whole of one force, say chemical action, 

 be supposed to be employed in producing its full equivalent of 

 another force, say heat ; then as this heat is capable in its turn of 

 reproducing chemical action, and, in the limit, a quantity equal or 

 at least only infinitely short of the initial force ; if this could at the 

 same time produce independently another force, say magnetism ; we 

 could, by adding this to the total heat, get more than the original 

 chemical action, and thus create force or obtain perpetual motion. 



The impossibility of perpetual motion thus becomes a valuable 

 test of the approach that in any experiment we may have made to 

 eliminating the whole power which a given natural force is capable of 

 producing; it also serves, M'hen any new natural phsenomenon is dis- 

 covered, to enable us to ascertain how far this can be brought into re- 

 lation with those previously known . Thus when Moser discovered that 

 dissimilar metals would impress each other respectively with a faint 

 image of their superficial inequalities ; that, for instance, a copper 

 coin placed on a polished silver plate, even in the dark, would, after 

 a short time, leave on the silver plate an impression of its own 

 device, it occurred to Mr. Grove, that as this experiment showed a 

 physical radiation taking place between the metals, it would aflforda 

 reason for the eflfects produced in Volta's contact experiment, with- 

 out supposing a force without consumption or change in the matter 

 evolving it. This led him to try the effect of closely approximating 

 discs of zinc and copper without bringing them into metallic contact ; 

 and it was found that discs thus approximated, and then quickly 

 separated, affected the electroscope just as though they had been 

 brought into contact. Without giving any opinion as to what may 

 be the nature of the radiation in Moser's piiaenomena, this experi- 

 ment removes the difficulty presented by that of Volta to the 

 chemical theory of electricity. 



